Gasification system

ABSTRACT

A gasification system includes a countercurrent type heat exchanger that includes a low-temperature side flow channel through which a gasification feedstock flows, and a high-temperature side flow channel to which treated water in a supercritical state is introduced. The treated water raises a temperature of the gasification feedstock by exchanging heat with the gasification feedstock. The system further includes a reactor that gasifies the gasification feedstock, whose temperature has been raised by the countercurrent type heat exchanger, by heating and pressurizing the gasification feedstock to be in a supercritical state. The reactor discharges the gasification feedstock as treated water in the supercritical state. The system further includes a treated water flow channel that introduces, to the countercurrent type heat exchanger, the treated water that has been discharged from the reactor, and a feedstock introduction port that introduces the feedstock to the low-temperature side flow channel.

TECHNICAL FIELD

One or more embodiments of the invention relate to a gasification systemfor gasifying gasification feedstocks such as biomass by using a heatexchanger.

BACKGROUND ART

As a system for gasifying feedstocks such as biomass (Shochu (distilledliquor) residue, egg-laying hen droppings and the like) by using a heatexchanger, Patent Literatures 1 and 2 disclose techniques that raise thetemperature of water-containing biomass by exchanging heat withsupercritical water in a double-pipe heat exchanger and gasify thebiomass by heating the biomass by a predetermined reactor and burner.

CITATION LIST Patent Literature

PTL 1: Japanese Patent No. 4719864

PTL 2: Japanese Patent No. 4997546

SUMMARY OF THE INVENTION

In each of heat exchangers of Patent Literatures 1 and 2, thetemperature of a suspension including biomass is raised from roomtemperature to a high temperature of, for example, about 400° C.Further, an internal pressure of the heat exchanger is high such as 25MPa at this time.

However, in such a high-temperature and high pressure, specific heat atconstant pressure of water (suspension) becomes large, and thus heatexchange efficiency in the heat exchanger is deteriorated. For thisreason, there was a case where the efficiency of gasification wasdeteriorated.

One or more embodiments of the invention provide a gasification systemthat improves the heat exchange efficiency in the heat exchanger andthus gasifies a gasification feedstock efficiently.

One or more embodiments of the present invention provide a gasificationsystem including a countercurrent type heat exchanger configured toinclude a low-temperature side flow channel through which a gasificationfeedstock flows, and a high-temperature side flow channel to whichtreated water in a supercritical state is introduced, the treated waterraising a temperature of the gasification feedstock by exchanging heatwith the gasification feedstock, a gasification reactor configured togasify the gasification feedstock, whose temperature has been raised bythe countercurrent type heat exchanger, by heating and pressurizing thegasification feedstock to be in a supercritical state, the gasificationreactor being configured to discharge the gasification feedstock astreated water in the supercritical state, and a treated water flowchannel configured to introduce, to the countercurrent type heatexchanger, the treated water that has been discharged from thegasification reactor, the gasification system including: a feedstockintroducing means (e.g., feedstock introduction port) configured tointroduce the gasification feedstock to the low-temperature side flowchannel; and an external heating means (e.g., external heater)configured to extract, from the middle of the low-temperature side flowchannel, the gasification feedstock that has been introduced by thefeedstock introducing means, heat the extracted gasification feedstock,and return the heated gasification feedstock to a middle position on afeedstock downstream side of a position in which the gasificationfeedstock has been extracted.

According to one or more embodiments of the present invention, thegasification feedstock that has been introduced to the heat exchanger isextracted in the middle of the low-temperature side flow channel, andthe extracted gasification feedstock is heated and returned to thefeedstock downstream side in the low-temperature side flow channel,thereby it is possible to prevent the gasification feedstock fromflowing through the point, for example, in which the heat exchangeefficiency deteriorates. This can enhance the heat exchange efficiencyin the heat exchanger. Further, the gasification feedstock can begasified efficiently by heating the gasification feedstock by theexternal heating means which is provided outside the heat exchanger.

In another aspect of one or more embodiments of the present invention, aposition in which the extraction is performed is determined based on avalue of specific heat at constant pressure of the gasificationfeedstock, and the gasification feedstock is extracted from the positionthat has been determined.

According to one or more embodiments of the present invention, since theposition in which the extraction is performed is determined based on thespecific heat at constant pressure, for example, the gasificationfeedstock is extracted from a position in which a value of the specificheat at constant pressure is low in the heat exchanger, and thus theheat exchange efficiency can be certainly enhanced.

In another aspect of one or more embodiments of the present invention,the low-temperature side flow channel is configured to include alow-temperature zone in which a temperature of the gasificationfeedstock introduced by the gasification feedstock introducing means israised, and a high-temperature zone in which a temperature of thegasification feedstock that has passed through the low-temperature zoneis raised again, and the external heating means extracts thegasification feedstock from a high temperature end of thelow-temperature zone and returns the gasification feedstock to a lowtemperature end of the high-temperature zone.

As in one or more embodiments of the present invention, the gasificationfeedstock is extracted from the high temperature end of thelow-temperature zone, and the extracted gasification feedstock isreturned to the low temperature end of the high-temperature zone, sothat the temperature of the gasification feedstock can be certainlyraised without allowing the gasification feedstock to flow through atemperature zone in which the heat exchange efficiency is low. This canperform gasification efficiently.

It should be noted that, the specific heat at constant pressure of thegasification feedstock at the position in which the extraction isperformed is, for example, 10 kJ/kg·K or greater.

In another aspect of one or more embodiments of the present invention,heating by the external heating means is performed in a preheater thatpreheats the gasification feedstock whose temperature has been raised bythe countercurrent type heat exchanger.

According to one or more embodiments of the present invention, theheating of the gasification feedstock that has been extracted from thecountercurrent type heat exchanger is performed by the preheater, andthus energy to be generated in the gasification system can be usedefficiently.

According to one or more embodiments of the present invention, agasification system can be provided in which the heat exchangeefficiency in the heat exchanger can be enhanced, and thus thegasification feedstock is gasified efficiently.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A is a diagram showing a schematic configuration of a biomassgasification system 100 with supercritical water.

FIG. 1B a diagram illustrating an example of a double-pipe configurationin a heat exchanger 30.

FIG. 2 is a diagram showing the heat exchanger 30 in a case in which thelength of a double-pipe from an introduction port 31 to a discharge port32 of a gasification feedstock is set to 100.

FIG. 3 is a diagram showing an example of changes in temperature (“tubetemperature”) of the gasification feedstock that flows through alow-temperature side flow channel 36 and changes in temperature (“jackettemperature”) of treated water that flows through a high-temperatureside flow channel 37.

FIG. 4 is a diagram showing a relationship among temperature, pressure,and specific heat at constant pressure.

FIG. 5 is an example of the heat exchanger 30 configured so that amedium-temperature zone 72 does not exist.

FIG. 6 is a diagram illustrating appropriate positions for an extractingposition 33 and a return position 34 in the heat exchanger 30.

FIG. 7 is a diagram showing a relationship among temperature, pressure,and specific heat at constant pressure.

DETAILED DESCRIPTION

FIG. 1A is a diagram showing a schematic configuration of a biomassgasification system 100 with supercritical water, which is described asone or more embodiments of the present invention. As illustrated in FIG.1A, the gasification system 100 includes an regulation tank 1, a crusher2, a supply pump 3, a heat exchanger 30, a preheater 40, a gasificationreactor 50, a cooler 51, a pressure reducer 52, a gas-liquid separator60, a gas tank 61 or the like. The heat exchanger 30 and thegasification reactor are connected by piping 55.

The regulation tank 1 is a tank for mixing biomass, water and activatedcarbon, while regulating a mixing amount of water and activated carbonin accordance with such as types, amount, and water content of biomass.In the regulation tank 1, a gasification feedstock (suspension) isprepared by mixing biomass, activated carbon and water. Note that, theabove-mentioned biomass is water-containing biomass, for example, Shochuresidue, egg-laying hen droppings or the like. Further, other non-metalcatalysts may be mixed instead of the activated carbon, for example,zeolite may be used, and a mixture thereof may also be used. Note that,powder with an average particle size of 200 μm or less may be used as anon-metal catalyst, and may be a porous catalyst.

The crusher 2 is a device that crushes biomass in the suspension, whichhas been prepared in the regulation tank 1, into a uniform size inadvance (an average particle size may be 500 μm or less, even 300 μm orless), and transfers the biomass to the supply pump 3.

The supply pump 3 is a device that supplies the suspension supplied fromthe crusher 2 to the exchanger 30. The supply pump 3 is, for example, ahigh pressure pump, Moineau pump and the like.

The heat exchanger 30 is a countercurrent type heat exchanger, and is adevice that uses heat of discharged matter (produced gas and ash whichare discharged from the gasification reactor 50, a non-metal catalystand water (supercritical water) or the like), which is discharged fromthe gasification reactor 50, to raise the temperature of thegasification feedstock (suspension) that is supplied from the supplypump 3. That is, this heat exchanger 30 includes a low-temperature sideflow channel 36 and a high-temperature side flow channel 37, throughwhich the gasification feedstock that is supplied from the supply pump 3flows. Treated water flows through the high-temperature side flowchannel 37, in which the treated water raises the temperature of thegasification feedstock by exchanging heat with the gasificationfeedstock that flows through the low-temperature side flow channel 36.

The above-mentioned discharged matter (treated water) is introduced tothe high-temperature side flow channel 37 through the piping 55.Meanwhile, the temperature of the suspension that has been introducedfrom the introduction port 31 is raised while flowing through thelow-temperature side flow channel 36, and the suspension is dischargedfrom the discharge port 32. Note that, the internal pressure of the heatexchanger 30 is set to about 25 MPa.

The heat exchanger 30 is, for example, a double-pipe heat exchanger.FIG. 1B is a diagram illustrating an example of a double-pipeconfiguration in the heat exchanger 30. As illustrated in FIG. 1B, thelow-temperature side flow channel 36 is provided as an inner pipe of thedouble-pipe, and the high-temperature side flow channel 37 is providedas an outer pipe of the double-pipe.

Referring back to FIG. 1A, the preheater 40 is a device that heats thesuspension to a predetermined temperature by burning such as producedgas, fuel gas (for example LPG), and oxygen gas which have beenaccumulated in the gas tank 61.

The gasification reactor 50 is, for example, a tubular reactor, afluidized-bed reactor or the like, and is a device for gasifying biomassin a suspension with supercritical water. This gasification uses theabove-stated non-metal catalyst and is performed at a temperature andunder a pressure (for example, 600° C. or greater, within 25 to 35 Mpa)which can enhance reaction efficiency. By treating biomass withsupercritical water in this way, the biomass can be decomposed toproduce gases such as hydrogen gas, methane, ethane, and ethylene.

The cooler 51 is a device for cooling the discharged matter that isdischarged from the gasification reactor 50.

The pressure reducer 52 is a device for reducing the pressure of theproduced gas and the like of the discharged matter that is dischargedfrom the gasification reactor 50.

The gas-liquid separator 60 is a device that separates the dischargedmatter, which is discharged from the gasification reactor 50, into a gascomponent (produced gas) and a liquid component (ash, activated carbon,and a mixed liquid containing water).

The gas tank 61 is a container (for example, a pressure resistantcontainer) that accumulates a gas component (produced gas) that isseparated by the gas-liquid separator 60.

The heater 62 that is provided in the gasification reactor 50 is adevice that burns, in the gas containing oxygen, a part of the producedgas accumulated in the gas tank 61 or fuel gas (for example, LPG and thelike) to heat the gasification reactor 50, and thus heats the suspensionto a predetermined temperature. Further, the heater 63 provided in thepreheater 40 is a device that burns, in the gas containing oxygen, apart of the produced gas accumulated in the gas tank 61 or fuel gas (forexample, LPG and the like) to heat the preheater 40, and thus heats thesuspension to a predetermined temperature. The heaters 62 and 63 areexisting devices, such as a burner, that burn fuel gas for heating.

In such a gasification system 100, water that flows through thehigh-temperature side flow channel 37 of the heat exchanger 30 istreated water in a supercritical state, which is discharged from thegasification reactor 50, as described above, and the temperature thereofis a high temperature such as at about 600° C. Further, the internalpressure of the heat exchanger 30 is also a high pressure which is 25MPa. In this high-temperature and high-pressure condition, there is acase where a temperature of the gasification feedstock is notsufficiently raised in the heat exchanger 30.

FIG. 3 is a diagram showing an example of changes in temperature (“tubetemperature”) of the gasification feedstock that flows through thelow-temperature side flow channel 36 and changes in temperature (“jackettemperature”) of the treated water that flows through thehigh-temperature side flow channel 37 in using the heat exchanger 30(see FIG. 2) when the entire length of a double-pipe from theintroduction port 31 to the discharge port 32 is set to 100. Asillustrated in FIG. 3, when treated water of about 600° C. is introducedto the heat exchanger 30, three zones including a low-temperature zone71, a medium-temperature zone 72 and a high-temperature zone 73 areformed in the heat exchanger 30 in the flowing order of the gasificationfeedstock (in order closer to the introduction port 31). In other words,in the low-temperature zone 71, the temperature of the gasificationfeedstock introduced from the introduction port 31 is rapidly raisedfrom about 25° C. to about 380°. However, in the medium-temperature zone72, the temperature of the gasification feedstock remains within apredetermined range and hardly rises (remains at about 380° C.). Then,in the high-temperature zone 73, the temperature of the gasificationfeedstock is raised again and reaches about 400° C. rapidly.

Thus, although the temperature of the gasification feedstock is rapidlyraised in the low-temperature zone 71 and the high-temperature zone 73,the temperature of the gasification feedstock is hardly raised in themedium-temperature zone 72, and thus the heat exchange treatment in theheat exchanger 30 is inefficient as a whole. The length of themedium-temperature zone 72 exceeds 50 percent of the entire length ofthe double-pipe of the heat exchanger 30 in some cases, this results ina reduction in the heat exchange efficiency of the heat exchanger 30especially in those cases.

The reasons that the medium-temperature zone 72 exists are as follows.FIG. 4 is a diagram showing a relationship among the temperature ofwater, pressure and specific heat at constant pressure. As illustratedin FIG. 4, when the internal pressure of the heat exchanger 30 is 25MPa, the specific heat at constant pressure takes a specifically highvalue (reaches its peak) at about 380° C., and thus the temperature ofthe gasification feedstock having such a temperature is not easilyraised. Further, also in the treated water that exchanges heat with thegasification feedstock, the specific heat at constant pressure reachesits peak at about 380° C. (more precisely, reaches its peak at somewhatlower temperature than the case of the gasification feedstock due to apressure loss in the double-pipe) as in the case of the gasificationfeedstock.

Then, the present inventors conceive that, if the heat exchanger 30 isconfigured so that a zone (a zone in which the temperature of thegasification feedstock is about 380° C. in the example described above)in which the temperature of the gasification feedstock is hardly raiseddoes not exist in the heat exchanger 30, in other words, so that themedium-temperature zone 72 does not exist, the heat exchange efficiencyin the heat exchanger 30 can be enhanced.

FIG. 5 illustrates one example of the heat exchanger 30 having such aconfiguration. As illustrated in FIG. 5, an external heating means 35for heating the gasification feedstock is provided outside the heatexchanger 30. In other words, a flow channel is changed in a manner inwhich, the gasification feedstock is extracted from a predeterminedposition 33 (hereinafter, referred to as an extracting position 33) ofthe low-temperature side flow channel 36 as shown by a reference number35 a, the extracted gasification feedstock is heated by heat of thepreheater 40 as shown by a reference number 35 b, and the heatedgasification feedstock is returned to a predetermined position 34(hereinafter, referred to as a return position 34) of thelow-temperature flow channel 36, which is arranged on a feedstockdownstream side of the extracting position 33 as shown by a referencenumber 35 c. This change of the flow channel is performed, for example,by connecting between the extracting position 33 and the preheater 40with piping so as to allow the gasification feedstock to flowtherethrough, and by connecting between the preheater 40 and the returnposition 34 with piping so as to allow the gasification feedstock toflow therethrough.

Specifically, the extracting position 33 and the return position 34described above are positions as follows. That is, as illustrated inFIG. 5, the extracting position 33 is a position in which a temperatureTc of the gasification feedstock becomes 370° C., and a temperature Tdof the treated water becomes 375° C. (that is, a high temperature end ofthe low-temperature zone 71, and a boundary part with themedium-temperature zone 72). Further, the return position 34 is aposition in which a temperature Te of the gasification feedstock becomes385° C., and a temperature Tf of the treated water becomes 390° C. (thatis, a low temperature end of the high-temperature zone 73, and aboundary part with the medium-temperature zone 72).

Note that, in response to such a change of the flow channel of thelow-temperature side flow channel 36, the flow channel of thehigh-temperature side flow channel 37 is also changed. That is, asillustrated in FIG. 5, the flow channel is configured so that theextracting position 33 and the return position 34 are connected withbypass piping 38, and the treated water directly flows from the returnposition 34 to the extracting position 33. Further, a surplus portion 39of the piping is removed due to the above-mentioned change of the flowchannel.

As described above, the extracting position 33 is provided at a boundarypart between a low-temperature area 71 and a medium-temperature area 72,and the return position 34 is provided at a boundary part between themedium-temperature area 72 and a high-temperature area 73, so that theheat exchange efficiency in the heat exchanger 30 can be enhanced andthe temperature of the gasification feedstock can be certainly raised.

Further, in this way, in the heat exchanger 30, an area does not existin which the temperature of the gasification feedstock becomes about380° C. that is a temperature at which a heat exchange rate of fluidreduces. In such a temperature, tar is produced in the double-pipe, andthe inner pipe (low-temperature side flow channel 36) and the outer pipe(high-temperature side flow channel 37) are easily clogged. Thus, inorder to avoid this, by providing the extracting position 33 and thereturn position 34 as stated above, production of tar can be suppressedand the piping can be prevented from being clogged, so that reliabilityof the gasification system 100 can be improved.

Further, since expensive and thick-walled piping is generally used forthe heat exchanger 30 to resist a high-temperature and high-pressurecondition, incidental expenses associated with maintenance of piping orthe like can be suppressed by performing such a change of the flowchannel that the medium-temperature zone 72 is omitted as stated above.

Further, the heating of the gasification feedstock that has beenextracted from the heat exchanger 30 is performed by the preheater 40,and thus energy efficiency in the gasification system 100 can beenhanced. Further, new introduction of a heating facility is notnecessary, and it is possible to prevent a cost from increasing.

In the example described above, the position in which the temperature ofthe gasification feedstock becomes about 370° C. is referred to as theextracting position 33, and the position in which the temperature of thegasification feedstock becomes about 385° C. is referred to as thereturn position 34. However, the extracting position 33 and the returnposition 34 are not limited to those positions. That is, the extractingposition 33 may be a boundary part between the low-temperature zone 71and the medium-temperature zone 72. Further, the return position 34 maybe a boundary part between the medium-temperature zone 72 and thehigh-temperature zone 73.

FIG. 6 is a diagram illustrating appropriate positions for theextracting position 33 and the return position 34 in the heat exchanger30. As illustrated in FIG. 6, the extracting position 33 may be arrangedsomewhere at a position in which the specific heat at constant pressureis relatively high (for example, in a range indicated by a referencenumber 33 a to a reference number 33 b) near the point in which thespecific heat at constant pressure of the gasification feedstock reachesa peak value at the closer side to the introduction port 31 (the pointin which the temperature of the gasification feedstock becomes about380° C.). For example, the extracting position 33 is such a positionthat the specific heat at constant pressure becomes 10 kJ/kg·K orgreater.

On the other hand, the return position 34 may be arranged somewhere at aposition in which the specific heat at constant pressure is relativelyhigh (for example, in a range indicated by a reference number 34 a to areference number 34 b) near the point in which the specific heat atconstant pressure of the gasification feedstock reaches a peak value atthe closer side to the discharge port 32 (the point in which thetemperature of the gasification feedstock becomes about 380° C.). Forexample, the return position is such a position that the specific heatat constant pressure becomes 10 kJ/kg·K.

Note that, in the above description, the internal pressure of the heatexchanger 30 is assumed to be 25 MPa. However, the internal pressure ofthe heat exchanger 30 may vary. If the internal pressure varies, a peaktemperature of the specific heat at constant pressure also varies (seeFIG. 4), and thus, when the internal pressure of the heat exchanger 30varies, the extracting position 33 is regulated in response thereto.

Next, how to determine the extracting position 33 in a case in which theinternal pressure of the heat exchanger 30 varies will be described.

FIG. 7 is a diagram showing a relationship among temperature of water,pressure and specific heat at constant pressure, which is used fordetermining the extracting position 33. As illustrated in FIG. 7, acurved surface 74 indicates an aggregation of plots of temperature andpressure at which the specific heat at constant pressure exceeds apredetermined value. It is possible to determine an appropriateextracting position 33 by reading out, from the curved surface 74, atemperature corresponding to the current pressure of the heat exchanger30.

As stated above, even when the internal pressure of the heat exchanger30 varies, it is possible to enhance the heat exchange efficiency in theheat exchanger 30 by determining the extracting position 33 and thereturn position 34 on the basis of values of the specific heat atconstant pressure.

As described above, according to the gasification system 100 of one ormore embodiments of the invention, the gasification feedstock introducedto the heat exchanger 30 is extracted in the middle of thelow-temperature side flow channel 36, the extracted gasificationfeedstock is heated and returned in the middle of the low-temperatureside flow channel 36, and thus, for example, it becomes possible toprevent the gasification feedstock from flowing through the point inwhich the heat exchange efficiency deteriorates. This can enhance theheat exchange efficiency in the heat exchanger 30. Further, thegasification feedstock is heated in the external heating means(preheater 40) which is provided outside the heat exchanger 30, and thusthe gasification feedstock can be efficiently gasified. Moreover, newintroduction of a heating facility is not necessary, and it is possibleto prevent a cost from increasing.

Further, since the position where the extraction is performed(extracting position 33) is determined based on the specific heat atconstant pressure, the heat exchange efficiency can be certainlyenhanced by, for example, extracting the gasification feedstock from aposition in which the specific heat at constant pressure is low in theheat exchanger 30.

Further, since the gasification feedstock is extracted from the boundarypart between the low-temperature zone 71 and the medium-temperature zone72, and the extracted gasification feedstock is returned to the boundarypart between the medium-temperature zone 72 and the high-temperaturezone 73, the temperature of the gasification feedstock can be certainlyraised without allowing the gasification feedstock to flow through themedium-temperature zone 72 in which the heat exchange efficiency is low.This can perform gasification efficiently.

The above description of one or more embodiments of the invention is tofacilitate understanding of one or more embodiments of the presentinvention, and does not limit the present invention. The presentinvention may be modified and improved without departing from the scopethereof, and the present invention includes equivalents thereof.

For example, the double-pipe heat exchanger has been adopted as the heatexchanger 30 in one or more embodiments of the invention. However, othertypes of heat exchangers may be adopted, as long as the heat exchangeris a countercurrent system.

Further, in one or more embodiments of the invention, a method of usingthe preheater 40 that is an existing facility is described as a means ofheating the gasification feedstock that has been extracted from theextracting position 33. However, the gasification feedstock may beheated by newly providing an external heating means (a heater or thelike).

Although the disclosure has been described with respect to only alimited number of embodiments, those skilled in the art, having benefitof this disclosure, will appreciate that various other embodiments maybe devised without departing from the scope of the present invention.Accordingly, the scope of the invention should be limited only by theattached claims

REFERENCE SIGNS LIST

1 regulation tank, 2 crusher, 3 supply pump, 30 heat exchanger, 31introduction port, 32 discharge port, 33 extracting position, 34 returnposition, 35 external heating means, 36 low-temperature side flowchannel, 37 high-temperature side flow channel, 38 bypass piping, 39surplus portion, 40 preheater, 50 gasification reactor, 51 cooler, 52pressure reducer, 55 piping, 60 gas-liquid separator, 61 gas tank, 62heater, 63 heater, 71 low-temperature zone, 72 medium-temperature zone,73 high-temperature zone, 74 a curved surface, 100 gasification system

1. A gasification system comprising: a countercurrent type heatexchanger that includes a low-temperature side flow channel throughwhich a gasification feedstock flows, and a high-temperature side flowchannel to which treated water in a supercritical state is introduced,wherein the treated water raises a temperature of the gasificationfeedstock by exchanging heat with the gasification feedstock; agasification reactor that gasifies the gasification feedstock, whosetemperature has been raised by the countercurrent type heat exchanger,by heating and pressurizing the gasification feedstock to be in asupercritical state, wherein the gasification reactor discharges thegasification feedstock as treated water in the supercritical state; atreated water flow channel that introduces, to the countercurrent typeheat exchanger, the treated water that has been discharged from thegasification reactor; a feedstock introduction port that introduces thegasification feedstock to the low-temperature side flow channel; and anexternal heater that extracts, from the middle of the low-temperatureside flow channel, the gasification feedstock that has been introducedby the feedstock introduction port, heats an extracted gasificationfeedstock, and returns a heated gasification feedstock to a middleposition on a feedstock downstream side of a position in which thegasification feedstock has been extracted.
 2. The gasification systemaccording to claim 1, wherein a position in which the extraction isperformed is determined based on a value of specific heat at constantpressure of the gasification feedstock, and the gasification feedstockis extracted from the position that has been determined.
 3. Thegasification system according to claim 1, wherein specific heat atconstant pressure of the water at the position in which the extractionis performed is 10 kJ/kg·K or greater.
 4. The gasification systemaccording to claim 1, wherein the low-temperature side flow channelincludes a low-temperature zone in which a temperature of thegasification feedstock introduced by the feedstock introduction port israised, and a high-temperature zone in which a temperature of thegasification feedstock that has passed through the low-temperature zoneis raised again, and the external heater extracts the gasificationfeedstock from a high temperature end of the low-temperature zone andreturns the gasification feedstock to a low temperature end of thehigh-temperature zone.
 5. The gasification system according to claim 1,wherein heating by the external heater is performed in a preheater thatpreheats the gasification feedstock whose temperature has been raised bythe countercurrent type heat exchanger.